Combined Effect Of Chlortetracycline And Oxytetracycline On Biological Phosphorus Removal And Microbial Activity

Antibiotics are ubiquitous pollutants in the environment,which are biologically harmful and seriously threaten the life safety of microorganisms.Antibiotics in the environment do not exist alone,but often exist in the form of mixtures,forming mixed pollutants with different ratios and concentrations.The effect of mixed pollutants on microorganisms is not simply superimposed,but there are more complex combined effects,which may cause more serious harm.Biological phosphorus removal is the main way of sewage phosphorus removal,and microbial activity directly affects the effect of sewage biological phosphorus removal.Therefore,it is very important to explore the combined effect of antibiotic mixture on microbial activity in biological phosphorus removal.At present,there are few studies on the combined effect of antibiotic mixture on biological phosphorus removal from sewage.Therefore,in order to explore the combined effect of antibiotic mixture on biological phosphorus removal and microbial activity.In this experiment,chlortetracycline and oxytetracycline with high detection rate in sewage treatment plant were selected as typical pollutants.Firstly,the inhibitory effects of different concentrations of chlortetracycline and oxytetracycline on the specific phosphorus uptake rate of biological phosphorus removal microorganisms were measured.The concentration effect curve of pollutants was fitted by nonlinear regression equation.The half effective concentrations of chlortetracycline and oxytetracycline were calculated.Three kinds of ratiometric mixed pollutants were designed by Equ-Ray.Then24 mixed pollutants were designed by dilution factor method.The inhibitory effect of mixed pollutants on biological phosphorus removal and microbial activity was measured.The effects of mixed pollutants are predicted by concentration addition model and independent action model.The combined effect relationship of chlortetracycline and oxytetracycline mixture on biological phosphorus removal and microbial activity inhibition effect was analyzed.To provide analytical methods and theoretical basis for in-depth study of the effect of chlortetracycline and oxytetracycline mixture on biological phosphorus removal microorganisms.The main results of the study are as follows:（1）A sequencing batch reactor was used to study the effect of chlortetracycline and oxytetracycline on biological phosphorus removal system.The influent orthophosphate concentration of the reactor is maintained at about 8 mg/L and the influent COD concentration is maintained at about 200 mg/L.When the concentration of chlortetracycline or oxytetracycline is less than 15 mg/L,the concentration of orthophosphate in effluent increases gradually with the increase of action time.When the action concentration of chlortetracycline or oxytetracycline is greater than 15 mg/L,with the increase of action time,the concentration of orthophosphate in effluent first increases and then decreases to about 8 mg/L.（2）The inhibitory effect of chlortetracycline and oxytetracycline on the specific phosphorus uptake rate of biological phosphorus removal microorganisms increased gradually with the increase of action time and concentration.When the concentration of chlortetracycline and oxytetracycline was 40 mg/L and the action time was 96 h,the maximum inhibitory effect of chlortetracycline on the specific phosphorus uptake rate of biological phosphorus removal microorganisms was 96.43%,and the maximum inhibitory effect of oxytetracycline on the specific phosphorus uptake rate of biological phosphorus removal microorganisms was 90.21%.（3）The inhibitory effects of chlortetracycline and oxytetracycline on alkaline phosphatase activity,acid phosphatase activity,catalase activity and electron transport system activity of biological phosphorus removal microorganisms also increased gradually with the increase of action time and concentration of pollutants.Among them,the maximum inhibitory effects of chlortetracycline on alkaline phosphatase activity,acid phosphatase activity,catalase activity and electron transport system activity were 98.41%,91.35%,89.62% and 95.14%.The maximum inhibitory effects of oxytetracycline on alkaline phosphatase activity,acid phosphatase activity,catalase activity and electron transport system activity were 93.17%,84.26%,83.90% and 88.39%.（4）The inhibitory effect of chlortetracycline and oxytetracycline mixture on the specific phosphorus uptake rate of biological phosphorus removal microorganisms increased with the increase of action time and concentration of the mixture.It has a certain time dependence and concentration dependence.The concentration addition model prediction curve and the independent action model prediction curve are both located above the confidence interval of the fitted concentration effect curve of the actual measured data.The prediction effect of concentration addition model is relatively good.Using the concentration addition model,the combined effect of chlortetracycline and oxytetracycline mixture on the inhibitory effect relationship of the specific phosphorus uptake rate of biological phosphorus removal microorganisms belongs to competitive antagonism.（5）The inhibitory effect of the mixture of chlortetracycline and oxytetracycline on alkaline phosphatase activity,acid phosphatase activity,catalase activity and electron transport system activity of biological phosphorus removing microorganisms at the three ratios gradually increased with the increase of the mixture action time and the action concentration.The concentration addition model and independent action model were used for prediction.It is found that the prediction effect of the independent action model is far better than that of the concentration addition model.According to the analysis of concentration addition model,the combined effect relationship of chlortetracycline and oxytetracycline mixture on the inhibition of alkaline phosphatase activity and electron transport system activity of biological phosphorus removal microorganisms belongs to competitive antagonism.The combined effect relationship of chlortetracycline and oxytetracycline mixture on the inhibition of acid phosphatase activity and catalase activity of biological phosphorus removal microorganisms belongs to additive effect.The effects of chlortetracycline,oxytetracycline and their mixed pollutants on biological phosphorus removal and microbial activity were studied.To explore the inhibitory effect of chlortetracycline,oxytetracycline and their mixture on biological phosphorus removal and microbial activity with the change of action time and concentration.The prediction effects of concentration addition model and independent action model are analyzed.To explore the combined effect relationship of chlortetracycline and oxytetracycline mixture on biological phosphorus removal microorganisms and their activity inhibition effect.Figure [32] Table [9] Reference 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